Risk of HIV or second syphilis infection in Danish men with newly acquired syphilis in the period 2000–2010

Objectives Risk of subsequent diagnosis of HIV in persons diagnosed with newly acquired syphilis, and syphilis in HIV-infected persons, are of interest as these infections are markers of unsafe sex. Methods From a nationwide register, all Danish men aged >16 years diagnosed with syphilis in the period 2000–2010 (n=1217) were identified, and subsequently data on HIV status was extracted from the Danish HIV Cohort Study. We used Kaplan–Meier analysis to estimate the 5-year risk of HIV and second syphilis infection, and Cox regression to determine incidence rate ratios (IRR). Results The 5-year risk of HIV diagnosis was 9.8% (95% CI 7.0% to 12.6%). Those with a second diagnosis of syphilis had a higher risk of being diagnosed with HIV (IRR=3.1, 95% CI 1.2 to 8.0). The 5-year risk for a second diagnosis of syphilis was 14.8% (95% CI 12.1% to 17.4%) and HIV-infected persons had a higher risk of a second syphilis diagnosis (IRR=4.0, 95% CI 2.8 to 5.9). Sixty-five percent of the persons were men having sex with men (MSM). Thirty-four percent of the HIV-infected persons had viral load >1000 copies/ml at time of syphilis diagnosis. Conclusions The substantial risks of syphilis and HIV infection in men diagnosed with one of these sexually transmitted diseases indicate a high frequency of unsafe sex in the Danish MSM population. As one-third of the HIV-infected persons diagnosed with syphilis had high viral loads, our data support initiation of antiretroviral therapy in all HIV-infected MSM to reduce HIV transmission.